Multi-ratio transmission

ABSTRACT

A multi-stage transmission having eight forward and one reverse gear including planetary gears, shafts, and shift elements. The sun gear of gearset (P 1 ) couples the third shaft ( 3 ) and the ring gear of gearset (P 3 ), and can couple the housing via brake ( 03 ). The input shaft couples the carrier of gearset (P 1 ) and can couple, via clutch ( 15 ), shaft ( 5 ), which couples the sun gear of gearset (P 3 ) and can couple, via clutch ( 57 ), shaft ( 7 ) that couples the ring gear of gearset (P 3 ). Shaft ( 6 ) couples the ring and sun gears of respective gearsets (P 1,  P 2 ). Shaft ( 8 ) couples the carrier and the sun gear of respective gearsets (P 3,  P 4 ). Shaft ( 4 ) couples the carrier of gearset (P 4 ) and can couple, via brake ( 04 ), the housing. The output shaft couples the ring gear of gearset (P 4 ) and the carrier of gearset (P 2 ). Clutch ( 56 ) detachably connects shafts ( 5, 6 ).

This application is a National Stage completion of PCT/EP2013/050349filed Jan. 10, 2013, which claims priority from German patentapplication serial no. 10 2012 201 678.3 filed Feb. 6, 2012.

FIELD OF THE INVENTION

The present invention relates to a multi-stage transmission in planetarydesign, in particular an automatic transmission for a motor vehicle.

BACKGROUND OF THE INVENTION

According to the prior art, automatic transmissions, in particular formotor vehicles, comprise planetary gear sets, which are shifted by meansof friction- or rather shift-elements, such as clutches and brakes, andwhich are typically connected to a start-up element that is subject to aslip effect and that is optionally provided with a bypass clutch, suchas a hydrodynamic torque converter or a hydraulic clutch.

Such an automatic transmission is known from DE 199 12 480 34 by theApplicant for example. This transmission comprises three single-carriageplanetary gear sets as well as three brakes and two clutches for theshifting of six forward gears and one reverse gear, an input drive shaftand an output shaft, wherein the carrier of the first planetary gear setis permanently connected to the ring gear of the second planetary gearset, and the carrier of the second planetary gear set is permanentlyconnected to the ring gear of the third planetary gear set, and theinput drive shaft is directly connected to the sun gear of the secondplanetary gear set.

In addition, in the known transmission, it is provided that the inputdrive shaft can be connected by means of the first clutch to the sungear of the first planetary gear set, and can be connected by means ofthe second clutch to the carrier of the first planetary set, wherein thesun gear of the first planetary gear set can be connected by means ofthe first brake to a housing of the transmission, and the carrier of thefirst planetary gear set can be connected by means of the second braketo the housing of the transmission, wherein the sun gear of the thirdplanetary gear set can be connected by means of the third brake to thehousing of the transmission. The output shaft of the transmission ispermanently connected to the carrier of the third planetary gear set andto the ring gear of the first planetary gear set.

In addition, a 9-speed multi-stage transmission is known from DE 29 36969 A1; it comprises eight shift elements and four planetary gear sets,wherein a planetary gear set serves as a front mounted transmission andthe main gearing has a Simpson set and a further planetary gear setwhich serves as a reverse gear.

Further multi-stage transmissions are known to the Applicant, forexample from DE 10 2005 010 210 A1 and DE 10 2006 006 637 A1.

Automatic vehicle transmissions in planetary design in general havealready been described in the prior art and are subject to constantfurther development and improvement. These transmissions should have lowconstruction costs, in particular a low number of shift elements, andwith a sequential method of shifting, should avoid double shifting, i.e.a connection or, respectively, disconnection of two shift elements, sothat when shifting in defined groups of gears, only one respective shiftelement is shifted.

A multi-stage transmission in planetary design is known from DE 10 2008000 428 A1 provided by the Applicant, which has an input drive and anoutput drive, which is disposed in a housing. In the case of the knowntransmission, at least four planetary gear sets, referred to in thefollowing as the first, second, third and fourth planetary gear set, atleast eight rotatable shafts, referred to in the following as the inputdrive shaft, output shaft, third, fourth, fifth, sixth, seventh andeighth shaft, as well as at least six shift elements, comprising brakesand clutches, are provided, the selective meshing of which producesdifferent transmission ratios between the input drive and the outputdrive, so that preferably nine forward gears and one reverse gear can beimplemented,

The first and the second planetary gear set, which are preferablydesigned as a minus planetary gear sets, this having a negativestationary transmission ratio, form a shiftable front mounted gear setthereby, wherein the third and the fourth planetary gear set form a maingear set.

In the case of the known multi-stage transmission, it is provided thatthe carriers of the first and of the second planetary gear set arecoupled with one another by means of a fourth shaft, which is connectedto an element of the main gear set, in that the ring gear of the firstplanetary gear set is coupled to the sun gear of the second planetarygear set by means of the eighth shaft, which can be detachably connectedby means of a first clutch to the input drive shaft, and in that the sungear of the first planetary gear set can be connected by means of athird shaft through a first brake to a housing of the transmission andcan be detachably connected by means of a second clutch to the inputdrive shaft, wherein the ring gear of the second planetary gear set canbe coupled by means of the fifth shaft through a second brake to ahousing of the transmission. In addition, the seventh shaft ispermanently connected to at least one element of the main gear set andcan be connected by means of a third brake to the housing of thetransmission, wherein the sixth shaft is permanently connected to atleast one additional element of the main gear set and is detachablyconnected by means of a third clutch to the input drive shaft; theoutput shaft is permanently connected to at least one additional elementof the main gear set.

In the known transmission, the fourth shaft is preferably permanentlyconnected to the ring gear of the third planetary gear set, wherein thesixth shaft is permanently connected to the ring gear of the fourthplanetary gear set and to the carrier of the third planetary gear set,and can be detachably connected by means of the third clutch to theinput drive shaft. In addition, the seventh shaft is permanentlyconnected to the sun gears of the third and fourth planetary gear set,and can be connected by means of the third brake to a housing of thetransmission. The output drive is produced thereby by means of theoutput shaft, which is permanently connected to the carrier of thefourth planetary gear set. In addition, the third and the fourthplanetary gear set can be assembled or, respectively, reduced into aRavigneaux gear set having a common carrier and a common ring gear.

SUMMARY OF THE INVENTION

The object of the present invention is to propose a multi-stagetransmission of the aforementioned type, which has eight forward gearsand one reverse gear having a sufficient transmission ratio, in whichthe construction costs and the installation size, in particular theinstallation length or, respectively, the weight, are optimized, and inaddition, the efficiency is improved in terms of drag and gearinglosses. In addition, in the case of the multi-stage transmissionaccording to the invention, low hogging moments should affect the shiftelements. In addition, the transmission should be suitable both for afront longitudinal design and for a front transverse design.

This object is achieved according to the invention by the featuresdescribed below.

Therefore, a multi-stage transmission according to the invention inplanetary design is proposed, which has an input drive and an outputdrive, which are disposed in a housing. In addition, at least fourplanetary gear sets, referred to in the following as the first, second,third and fourth planetary gear set, eight rotatable shafts, referred toin the following as the input drive shaft, output shaft, third, fourth,fifth, sixth, seventh and eighth shaft, and at least five shift elementspreferably designed as lamellar shift elements or as form fitting shiftelements comprising two brakes and three clutches, are provided, theselective meshing of which produces different transmission ratiosbetween the input drive and the output drive, so that preferably eightforward gears and one reverse gear can be implemented.

Viewed axially, the planetary gear sets are preferably disposed in thesequence of the first planetary gear set, the second planetary gear set,the third planetary gear set, and the fourth planetary gear set, whereinthe first, second and third planetary gear sets are preferably designedas minus planetary gear sets and wherein the fourth planetary gear setis preferably designed as a plus-planetary gear set. Within the contextof further embodiments of the invention, the axial sequence of theplanetary gear sets may be in any order.

Within the context of a further refinement of the invention, two of theplanetary gear sets are disposed one over the other when viewed in aradial direction, as a result of which a very short installation lengthis achieved, whereby the transmission can be installed in passengervehicles in a front transverse construction.

The second planetary gear set is hereby advantageously disposed over thefirst planetary gear set when viewed in a radial direction, wherein theplanetary gear sets in this case are disposed in the sequence of thefirst planetary gear set/second planetary gear set, the fourth planetarygear set, and the third planetary gear set when viewed in an axialdirection.

It is known that a simple minus planetary gear set comprises a sun gear,a ring gear and a carrier, on which planetary gears are rotatablymounted, each of which mesh with the sun gear and ring gear. When thecarrier is restrained, the ring gear hereby has a direction of rotationthat is opposite to that of the sun gear. By contrast, a simple plusplanetary gear set comprises a sun gear, a ring gear and a carrier, onwhich internal and external planetary gears are rotatably mounted,wherein all internal planetary gears mesh with the sun gear, and allexternal planetary gears mesh with the ring gear, wherein the internalplanetary gears each mesh with an external planetary gear. When thecarrier is held, the ring gear hereby has the same direction of rotationas the sun gear, and this results in a positive stationary transmissionratio.

According to the invention, the sun gear of the first planetary gear setis connected to the third shaft, which shaft can be coupled by means ofa first brake to the housing of the transmission and which is connectedto the ring gear of the third planetary gear set, wherein the inputdrive shaft is connected to the carrier of the first planetary gear setand can be detachably connected by means of a first clutch to the fifthshaft, which shaft is connected to the sun gear of the third planetarygear set and can be detachably connected by means of a second clutch tothe seventh shaft, the seventh shaft being connected to the ring gear ofthe second planetary gear set.

In addition, the ring gear of the first planetary gear set is connectedto the sixth shaft of the transmission, which shaft is connected to thesun gear of the second planetary gear set, wherein the eighth shaft isconnected to the carrier of the third planetary gear set and to the sungear of the fourth planetary gear set, and wherein the fourth shaft,which is connected to the carrier of the fourth planetary gear set, canbe coupled by means of a second brake to the housing of thetransmission.

In addition, the output shaft of the transmission is connected to thering gear of the fourth planetary gear set and to the carrier of thesecond planetary gear set, wherein, according to the invention, a thirdclutch is provided, which detachably connects the fifth shaft to thesixth shaft.

The design of the multi-stage transmission according to the inventionresults in transmission ratios that are especially suited for passengervehicles, as well as an increased overall gear ratio spread of themulti-stage transmission, which leads to an improvement in the drivingcomfort and a significant reduction in the fuel consumption.

Moreover, the construction costs are substantially reduced, in the caseof the multi-stage transmission according to the invention, by a lownumber of shift elements. With the multi-stage transmission according tothe invention, it is advantageously possible to perform a start-up usinga hydrodynamic converter, an external start-up clutch or also with othersuitable, external start-up elements. It is also conceivable that astart-up procedure can be made possible using a start-up element that isintegrated in the transmission. A shift element, which is actuated inthe first forward gear and in the reverse gear, is preferably suitedthereto.

In addition, in the multi-stage transmission according to the invention,a good degree of efficiency is created in the main drive gears in termsof drag and gearing losses,

In addition, there are low torques in the shift elements and in theplanetary gear sets of the multi-stage transmission, whereby theabrasive wear in the multi-stage transmission is advantageously reduced.Moreover, the low torques make correspondingly small dimensionspossible, whereby the necessary installation space and the associatedcosts are reduced. In addition, there are also low rotational speeds inthe shafts, the shift elements and the planetary gear sets.

Moreover, the transmission according to the invention is designed insuch a way that it can be adapted to different drive train embodimentsboth in the power flow direction, and in terms of spatialconsiderations.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in greater detail below with reference to theaccompanying Figures. Shown are:

FIG. 1: a schematic view of a first preferred embodiment of amulti-stage transmission according to the invention;

FIG. 2: a schematic view of a second preferred embodiment of a mu stagetransmission according to the invention; and

FIG. 3: an example of a shift pattern for a multi-stage transmissionpursuant to FIGS. 1 and 2;

FIG. 4: diagrammatically shows an electrical machine disposed on theinput shaft of the multi-stage transmission according to the invention;

FIG. 5: diagrammatically shows a clutch provided between an engine andthe multi-stage transmission according to the invention; and

FIG. 6: diagrammatically shows an electrical machine disposed parallelto the input shaft of the multi-stage transmission according to theinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates a multi-stage transmission according to the inventionhaving an input drive shaft 1, an output shaft 2 and four planetary gearsets P1, P2, P3 and P4, which are disposed in a housing G. In theexample shown in FIG. 1, the first, second and third planetary gear setP1, P2, P3 are designed as minus planetary gear sets, wherein the fourthplanetary gear set P4 is designed as a plus planetary gear set.According to the invention, at least one of the planetary gear sets P1,P2, P3 may be designed as a plus planetary gear set when, at the sametime, the carrier and ring gear connections are switched and the valueof the stationary transmission ratio is increased by 1 in comparison tothe design as a minus planetary gear.

In the case of the embodiment shown, when viewed in an axial direction,the planetary gear sets are disposed in the sequence of the firstplanetary gear set P1, the second planetary gear set P2, the thirdplanetary gear set P3, the fourth planetary gear set P4.

As can be seen in FIG. 1, five shift elements are provided, namely twobrakes 03, 04 and three clutches 15, 56, 57. The spatial arrangement ofthe shift elements can be arbitrary, and is only limited by thedimensions and the external shape. The clutches and the brakes of thetransmission are preferably designed as friction or form locking shiftelements.

A selective shifting of eight forward gears and one reverse gear can beachieved using these shift elements. The multi-stage transmissionaccording to the invention has a total of eight rotatable shafts, namelythe shafts 1, 2, 3, 4, 5, 6, 7 and 8, wherein the input drive shaftforms the first shaft 1 and the output shaft forms the second shaft 2 ofthe transmission. The output shaft 2 is preferably disposed coaxially tothe input drive shaft 1, whereby a front-longitudinal design can beachieved.

According to the invention, in the multi-stage transmission pursuant toFIG. 1, it is provided that the sun gear of the first planetary gear setP1 is connected to the third shaft 3, which shaft can be coupled bymeans of a first brake 03 to the housing G of the transmission, andwhich is connected to the ring gear of the third planetary gear set P3,wherein the input drive shaft 1 is connected to the carrier of the firstplanetary gear set P1 and can be detachably coupled by means of a firstclutch 15 to the fifth shaft 5, which shaft is connected to the sun gearof the third planetary gear set P3, and which can be detachablyconnected by means of a second clutch 57 to the seventh shaft 7, whichis connected to the ring gear of the third planetary gear set P3.

As can be seen in FIG. 1, the ring gear of the first planetary gear setP1 is connected to the sixth shaft 6, which shaft is connected to thesun gear of the second planetary gear set P2, wherein the eighth shaft 8is connected to the carrier of the third planetary gear set P3 and tothe sun gear of the fourth planetary gear set P4. The fourth shaft 4,which is connected to the carrier of the fourth planetary gear set P4,can be coupled by means of a second brake 04 to the housing G of thetransmission.

In addition, the output shaft 2 is connected to the ring gear of thefourth planetary gear set P4 and to the carrier of the second planetarygear set P2, wherein according to the invention, a third clutch 56 isprovided, which detachably connects the fifth shaft 5 to the sixth shaft6.

In the case of the example shown in FIG. 2, when viewed in a radialdirection, the second planetary gear set P2 is disposed above the firstplanetary gear set P1; when viewed in an axial direction, the planetarygear sets are disposed in the sequence of the first planetary gear setP1/second planetary gear set P2, the fourth planetary gear set P4, thethird planetary gear set P3.

When viewed in an axial direction, the first, second and third clutch15, 57, 56 are disposed next to one another, and can have a commonexternal lamellar carrier,

With reference to FIG. 2, the output drive is transverse to thelongitudinal input drive shaft 1; when viewed in an axial direction, theoutput shaft 2 is disposed between the first and the second planetarygear set P1, P2, which, when viewed in a radial direction, are disposedone over the other, and the fourth planetary gear set P4.

FIG. 3 illustrates an example of a shift pattern of a multi-stagetransmission pursuant to FIGS. 1 and 2. Three shift elements are engagedfor each speed. The shift pattern shows the respective transmissionratios i of the individual gear steps and the gear increments or stepchanges φ for the next higher speed to be determined therefrom, whereinthe value 8.040 represents the transmission ratio spread of thetransmission.

In the example shown, the values for the stationary transmission ratiosof the planetary gear sets P1, P2, P3, which are designed as minusplanetary gear sets, are −1.720, −1.630 and −1.580 respectively, whereinthe stationary transmission ratio of the fourth planetary gear set P4,which is designed as a plus—planetary gear set, is 1.970. It is clearfrom FIG. 2 that in the case of a sequential manner of shifting, onlyone shift element must be engaged, and one shift element must bedisengaged, since two adjacent gear steps use two shared shift elements.In addition, it is apparent that a large transmission ratio spread isobtained with small gear increments.

The first forward gear is created by engaging the first and second brake03, 04 and the first clutch 15, the second forward gear is created byengaging the first and second brake 03, 04 and the third clutch 56, thethird forward gear is created by engaging the second brake 04 and thefirst and third clutch 15, 56, the fourth forward gear is created byengaging the second brake 04 and the second and third clutch 57, 56, thefifth forward gear is created by engaging the second brake 04 and thefirst and second clutch 15, 57, the sixth forward gear is created byengaging the first, second and third clutch 15, 57, 56, the seventhforward gear is created by engaging the first brake 03 and the first andsecond clutch 15, 57 and the eighth forward gear is created by engagingthe first brake 03 and the second and third clutch 57, 56, wherein thereverse gear is created by engaging the first and second brake 03, 04and the second clutch 57.

Because the first and second brakes 03, 04 are engaged in the firstforward gear and in the reverse gear, these shift elements may be usedas start-up elements.

According to the invention, even with the same gear pattern, differentgear increments are created depending on the shift logic, so that anapplication or, respectively, vehicle-specific variation is madepossible.

Within the context of a refinement of the invention not shown here, anelectric machine may be provided, which is directly connected(diagrammatically shown in FIG. 4) or indirectly connected(diagrammatically shown in FIG. 6) by means of a gear step or a chaindrive to the input drive shaft 1 of the transmission. In addition, asdiagrammatically shown in FIG. 5 a fourth clutch may be provided, bymeans of which the internal combustion engine of the transmission can bedisconnected, whereby all gears of the transmission can be driven purelyelectrically.

According to the invention, it is also optionally possible to provideadditional freewheels at each suitable position of the multi-stagetransmission where applicable, for example between a shaft and thehousing, or in order to connect two shafts.

An axle differential and/or a distributor differential can be disposedon the input drive side or on the output drive side.

Within the context of an advantageous refinement of the invention, theinput drive shaft 1 can be separated by a clutch element from a drivemotor if needed, wherein a hydrodynamic converter, a hydraulic clutch, adry start-up clutch, a wet start-up clutch, a magnetic powder clutch ora centrifugal clutch can be used as a clutch element. It is alsopossible to dispose such a start-up element in the power flow directionbehind the transmission, wherein, in this case, the input drive shaft 1is constantly connected to the crank shaft of the drive motor.

In addition, the multi-stage transmission according to the inventionmakes it possible for a torsional vibration damper to be disposedbetween the drive motor and the transmission.

Within the context of a further embodiment of the invention not shownhere, a wear-free brake, for example such as a hydraulic or electricretarder or the like, can be disposed on each shaft, preferably on theinput drive shaft 1 or the output shaft 2, which is of particularimportance, especially for use in commercial vehicles. In addition, apower take-off drive may be provided on each shaft, preferably on theinput shaft 1 or the output shaft 2 to be driven by additional powerengines.

The friction elements used may be designed as power shiftable clutchesor brakes. In particular, force locking clutches or brakes, for examplesuch as lamellar clutches, band brakes and/or cone clutches may be used.

A further advantage of the multi-stage transmission put forward hereconsists in the fact that an electric machine can be attached to eachshaft as a generator and/or as an additional drive machine.

REFERENCE FIGURES

-   1 first shaft, input drive shaft-   2 second shaft, output shaft-   3 third shaft-   4 fourth shaft-   5 fifth shaft-   6 sixth shaft-   7 seventh shaft-   8 eighth shaft-   03 first brake-   04 second brake-   15 first clutch-   56 third clutch-   57 second clutch-   G housing-   P1 first planetary gear set-   P2 second planetary gear set-   P3 third planetary gear set-   P4 fourth planetary gear set-   i transmission ratio

φ step change

1-8. (canceled)
 9. A multi-stage automatic transmission for a motorvehicle, the transmission comprising: an input shaft (1) and an outputshaft (2); first, second, third and fourth planetary gear sets (P1, P2,P3, P4) being disposed in a housing (G), and each of the first, thesecond, the third and the fourth planetary gear sets comprising a sungear, a ring gear and a carrier; at least third, fourth, fifth, sixth,seventh and eighth rotatable shafts (3, 4, 5, 6, 7, 8); at least fiveshift elements (03, 04, 15, 56, 57) comprising first and second brakes(03, 04) and first, second, third and fourth clutches (15, 56, 57, 58)whose selective engagement results in different transmission ratiosbetween the input shaft (1) and the output shaft (2) so that eightforward gears and one reverse gear are implementable: the third shaft(3) being connected to both the sun gear of the first planetary gear set(P1) and the ring gear of the third planetary gear set (P3), and thethird shaft (3) being couplable by the first brake (03) to the housing(G); the input drive shaft (1) being connected to the carrier of thefirst planetary gear set (P1), the input drive shaft (1) beingdetachably connectable by the first clutch (15) to the fifth shaft (5),the fifth shaft (5) being connected to the sun gear of the thirdplanetary gear set (P3), the fifth shaft (5) being detachablyconnectable by the second clutch (57) to the seventh shaft (7), and theseventh shaft (7) being connected to the ring gear of the secondplanetary gear set (P2); the sixth shaft (6) being is connected to boththe ring gear of the first planetary gear set (P1) and the sun gear ofthe second planetary gear set (P2); the eighth shaft (8) being connectedto the carrier of the third planetary gear set (P3) and the sun gear ofthe fourth planetary gear set (P4), the fourth shaft (4) being connectedto the carrier of the fourth planetary gear set (P4) being couplable bythe second brake (04) to the housing (G); the output shaft (2) beingconnected to the ring gear of the fourth planetary gear set (P4) and tothe carrier of the second planetary gear set (P2); and the third clutch(56) detachably connecting the fifth shaft (5) to the sixth shaft (6).10. The multi-stage transmission according to claim 9, wherein thefirst, the second, and the third planetary gear sets (P1, P2, P3) aredesigned as minus planetary gear sets, and the fourth planetary gear set(P4) is designed as a plus planetary gear set.
 11. The multi-stagetransmission according to claim 9, wherein, when viewed in an axialdirection, the first, the second, the third and the fourth planetarygear sets (P1, P2, P3, P4) are disposed in a sequence of the firstplanetary gear set (P1), the second planetary gear set (P2), the thirdplanetary gear set (P3), and the fourth planetary gear set (P4).
 12. Themulti-stage transmission according to claim 9, wherein, when viewed in aradial direction, the second planetary gear set (P2) radial is disposedaround the first planetary gear set (P1).
 13. The multi-stagetransmission according to claim 12, wherein, when viewed in an axialdirection, the first, the second, the third and the fourth planetarygear sets are axially disposed in a sequence of both the first planetarygear set (P1) and the second planetary gear set (P2), followed by thefourth planetary gear set (P4), and then the third planetary gear set(P3).
 14. The multi-stage transmission according to claim 9, wherein anelectric machine is connected to the input drive shaft (1) of thetransmission, either directly, or by either a gear stage or a chaindrive.
 15. The multi-stage transmission according to claim 14, whereinan internal combustion engine is disconnectable from the transmission bya fourth clutch, whereby all transmission gears can be driven purelyelectrically.
 16. The multi-stage transmission according to claim 9,wherein a first forward gear is implemented by engagement of the firstand the second brakes (03, 04) and the first clutch (15), a secondforward gear is implemented by engagement of the first and the secondbrakes (03, 04) and the third clutch (56), a third forward gear isimplemented by engagement of the second brake (04) and the first and thethird clutches (15, 56), a fourth forward gear is implemented byengagement of the second brake (04) and the second and the thirdclutches (57, 56), a fifth forward gear is implemented by engagement ofthe second brake (04) and the first and the second clutches (15, 57), asixth forward gear is implemented by engagement of the first, the secondand the third clutches (15, 57, 56), a seventh forward gear isimplemented by engagement of the first brake (03) and the first and thesecond clutches (15, 57), an eighth forward gear is implemented byengagement of the first brake (03) and the second and third clutches(57, 56), and the reverse gear is implemented by engagement of the firstand the second brakes (03, 04) and the second clutch (57).
 17. Amulti-stage automatic transmission for a motor vehicle, the transmissioncomprising: an input shaft (1) and an output shaft (2); first, second,third and fourth planetary gear sets (P1, P2, P3, P4) being disposedwithin a housing (G), and each of the first, the second, the third andthe fourth planetary gear sets comprising a sun gear, a ring gear and acarrier; at least third, fourth, fifth, sixth, seventh and eighthrotatable shafts (3, 4, 5, 6, 7, 8); at least five shift elements (03,04, 15, 56, 57) comprising first and second brakes (03, 04) and first,second and third clutches (15, 56, 57), selective engagement of the atleast five shift elements results in different transmission ratiosbetween the input shaft (1) and the output shaft (2) so that eightforward gears and one reverse gear are implementable; the input shaft(1) being continuously connected to the carrier of the first planetarygear set (P1) and the input shaft (1) being connectable, via the firstclutch (15), to the fifth shaft (5); the output shaft (2) beingcontinuously connected to both the ring gear of the fourth planetarygear set (P4) and the carrier of the second planetary gear set (P2); thethird shaft (3) being continuously connected to the sun gear of thefirst planetary gear set (P1) and the ring gear of the third planetarygear set (P3) and the third shaft (3) being connectable, via the firstbrake (03), to the housing (G); the fourth shaft (4) being continuouslyconnected to the carrier of the fourth planetary gear set (P4) and thefourth shaft (4) being connectable, via the second brake (04), to thehousing (G); the fifth shaft (5) being continuously connected to the sungear of the third planetary gear set (P3), the fifth shaft (5) beingconnectable, via the second clutch (57), to the seventh shaft (7), andthe fifth shaft (5) being connectable, via the third clutch (56), to thesixth shaft (6); the sixth shaft (6) being continuously connected to thering gear of the first planetary gear set (P1) and the sun gear of thesecond planetary gear set (P2); the seventh shaft (7) being continuouslyconnected to the ring gear of the second planetary gear set (P2); andthe eighth shaft (8) being continuously connected to both the carrier ofthe third planetary gear set (P3) and the sun gear of the fourthplanetary gear set (P4).
 18. The multi-stage transmission according toclaim 17, wherein a first forward gear is implemented by engagement ofthe first and the second brakes (03, 04) and the first clutch (15), asecond forward gear is implemented by engagement of the first and thesecond brakes (03, 04) and the third clutch (56), a third forward gearis implemented by engagement of the second brake (04) and the first andthe third clutches (15, 56), a fourth forward gear is implemented byengagement of the second brake (04) and the second and the thirdclutches (57, 56), a fifth forward gear is implemented by engagement ofthe second brake (04) and the first and the second clutches (15, 57), asixth forward gear is implemented by engagement of the first, the secondand the third clutches (15, 57, 56), a seventh forward gear isimplemented by engagement of he first brake (03) and the first and thesecond clutches (15, 57), an eighth forward gear is implemented byengagement of the first brake (03) and the second and third clutches(57, 56), and the reverse gear is implemented by engagement of the firstand the second brakes (03, 04) and the second clutch (57).